Semiconductor device with air gap and method for fabricating the same

ABSTRACT

A semiconductor device includes a plurality of first conductive structures formed over a substrate, second conductive structures each formed between neighboring first conductive structures of the first conductive structures, air gaps each formed between the second conductive structures and the neighboring first conductive structures thereof, third conductive structures each capping a portion of the air gaps, and capping structures each capping the other portion of the air gaps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/106,787 filed on Dec. 15, 2013, which claims priority of KoreanPatent Application No. 10-2013-0091075, filed on Jul. 31 2013. Thedisclosure of each of the foregoing applications is incorporated hereinby reference in its entirety.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a semiconductordevice, and more particularly, to a semiconductor device including airgaps and a method for fabricating the semiconductor device.

2. Description of the Related Art

Semiconductor devices generally include a dielectric material interposedbetween neighboring conductive structures. As semiconductor devices arehighly integrated, the distance between conductive structures becomesnarrow, thus increasing parasitic capacitance. The increase in theparasitic capacitance deteriorates performance of a semiconductordevice.

Among the methods for decreasing the parasitic capacitance is a methodof reducing the dielectric constant of a dielectric material. However,since the dielectric material has a high dielectric constant, there is alimitation in decreasing the parasitic capacitance.

SUMMARY

Exemplary embodiments of the present invention are directed to asemiconductor device that may have decreased parasitic capacitancebetween neighboring conductive structures, and a method for fabricatingthe semiconductor device,

In accordance with an embodiment of the present invention, asemiconductor device includes a plurality of first conductive structuresformed over a substrate, one or more second conductive structures eachformed between neighboring first conductive structures of the firstconductive structures, one or more air gaps each formed between thesecond conductive structures and the neighboring first conductivestructures thereof, one or more third conductive structures each cappinga portion of the air gaps, and one or more capping structures eachcapping the other portion of the air gaps.

In accordance with another embodiment of the present invention, asemiconductor device includes an isolation structure formed over asubstrate and including one or more openings, one or more firstconductive structures each formed in the opening on the substrate, oneor more air gaps each formed between a sidewall of the first conductivestructure and a sidewall of the opening, one or more second conductivestructures each capping a portion of the air gap, and one or morecapping structures each capping the other portion of the air gap.

In accordance with a further embodiment of the present invention, amethod for fabricating a semiconductor device includes forming anisolation layer over a substrate, forming an opening by etching theisolation layer, forming a preliminary first conductive structure whichincludes a first conductive structure formed inside the opening and asacrificial spacer formed between a sidewall of the first conductivestructure and a sidewall of the opening, forming a second conductivestructure which covers a portion of the first conductive structure and aportion of the sacrificial spacer, forming an air gap by removing thesacrificial spacer, and forming a capping structure for capping aportion of the air gap.

In accordance with a still further embodiment of the present invention,a method for fabricating a semiconductor device includes forming aplurality of first conductive structures over a substrate, forming anisolation layer between the first conductive structures, forming one ormore openings by etching the isolation layer, forming one or morepreliminary second conductive structures in the respective openings,wherein the preliminary second conductive structure includes a secondconductive structure formed inside the opening and a sacrificial spacerformed between a sidewall of the second conductive structure and asidewall of the opening, forming one or more third conductive structuresover the respective preliminary second conductive structures, whereinthe third conductive structure covers a portion of the second conductivestructure and a portion of the sacrificial spacer, forming one or moreair gaps by removing the respective sacrificial spacers, and forming oneor more capping structures for capping respective the air gaps.According to an embodiment of the present invention, the parasiticcapacitance may be decreased by forming the air gap between conductivestructures.

According to an embodiment of the present invention, since the air gapis capped with a conductive structure and a capping structure, the airgap may be stably protected in the subsequent process.

According to an embodiment of the present invention, since an ohmiccontact layer is formed in a wide area, contact resistance may bedecreased.

According to an embodiment of the present invention, the resistance of aconductive structure may be decreased by increasing the volume of ametal-containing material included in the conductive structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view illustrating a semiconductor device inaccordance with a first embodiment of the present invention;

FIG. 1B is a cross-sectional view illustrating a semiconductor device inaccordance with a modified example of the first embodiment of thepresent invention;

FIG. 1C is a plan view illustrating the semiconductor device inaccordance with the first embodiment of the present invention and themodified example thereof;

FIGS. 2A to 2L are cross-sectional views describing a method forfabricating the semiconductor device in accordance with the firstembodiment of the present invention;

FIG. 3A is a cross-sectional view illustrating a semiconductor device inaccordance with a second embodiment of the present invention;

FIG. 3B is a cross-sectional view illustrating a semiconductor device inaccordance with a modified example of the second embodiment of thepresent invention;

FIG. 3C is a plan view illustrating the semiconductor device inaccordance with the second embodiment of the present invention and themodified example thereof;

FIGS. 4A to 4K are cross-sectional views describing a method forfabricating the semiconductor device in accordance with the secondembodiment of the present invention;

FIGS. 5A to 5D are cross-sectional views illustrating a comparativeexample of the second embodiment of the present invention;

FIG. 6A is a cross-sectional view illustrating a portion of a memorycell;

FIG. 6B is a plan view illustrating the memory cell of FIG. 6A;

FIG. 6C is a cross-sectional view illustrating the memory cell takenalong a line B-B′ of FIG. 6B;

FIGS. 7A to 7L are cross-sectional exemplarily describing a method forfabricating a memory cell;

FIG. 8 illustrates a memory card in accordance with an embodiment of thepresent invention; and

FIG. 9 illustrates an electronic system in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to a casewhere the first layer is formed directly on the second layer or thesubstrate but also a case where a third layer exists between the firstlayer and the second layer or the substrate. It is also noted that inthis specification, “connected/coupled” refers to one component not onlydirectly coupling another component but also indirectly coupling anothercomponent through an intermediate component. In addition, a singularform may include a plural form as long as it is not specificallymentioned in a sentence.

FIG. 1A is a cross-sectional view illustrating a semiconductor device inaccordance with a first embodiment of the present invention. FIG. 1B isa cross-sectional view illustrating a semiconductor device in accordancewith a modified example of the first embodiment of the presentinvention. FIG. 1C is a plan view illustrating the semiconductor devicein accordance with the first embodiment of the present invention and themodified example thereof.

Referring to FIG. 1A, an insulation layer 12 is formed over a substrate11, and then openings 13 are formed in the insulation layer 12. Theopenings 13 expose the surface of the substrate 11. A first conductivestructure 22 is formed in each opening 13. An air gap 23 is formedbetween sidewalls of the first conductive structure 22 and sidewalls ofthe opening 13. A second conductive structure 20 for capping a portionof the air gap 23 is formed, and a capping structure 24 is formed forcapping the other portion of the air gap 23, which is not capped by thesecond conductive structure 20.

The substrate 11 includes a semiconductor substrate. To be specific, thesubstrate 11 may be a silicon substrate, a silicon germanium substrate,or a Silicon On Insulator (SOI) substrate. The insulation layer 12includes a dielectric material. Specifically, the insulation layer 12includes a low-k dielectric material. The insulation layer 12 may be asilicon nitride layer or a silicon oxide layer. The insulation layer 12may be an inter-layer dielectric (ILD) layer.

The openings 13 may have a hole shape or a line shape. For example, theopenings 13 may be defined as contact holes, vias, through-holes,trenches, or recesses. When the opening 13 is a contact hole, the firstconductive structure 22 is a plug.

The first conductive structure 22 includes a first conductive pattern15, a second conductive pattern 18 and a third conductive pattern 19.The first conductive pattern 15 is formed by being recessed in theopening 13. The second conductive pattern 18 is formed over the firstconductive pattern 15, and the third conductive pattern 19 is formedover the second conductive pattern 18. The first conductive pattern 15occupies less volume than the third conductive pattern 19 in the firstconductive structure 22. The air gap 23 is formed between the sidewallsof the third conductive pattern 19 and the sidewalls of opening 13. Thefirst conductive pattern 15 includes a silicon-containing layer. Thefirst conductive pattern 15 may include polysilicon. The polysilicon maybe doped with an impurity. The second conductive pattern 18 and thethird conductive pattern 19 include a metal-containing layer. As anexample, the second conductive pattern 18 includes a metal silicide, andthe third conductive pattern 19 includes a metal layer. The secondconductive pattern 18 functions as an ohmic contact layer between thefirst conductive pattern 15 and the third conductive pattern 19. Thesecond conductive pattern 18 may include a cobalt silicide. The cobaltsilicide may be of a “CoSi₂” phase. The third conductive pattern 19 mayinclude tungsten. The first conductive structure 22 has a stackedstructure where a polysilicon layer, a cobalt silicide layer, and atungsten layer are stacked. Since the volume of the third conductivepattern 19 is greater than that of the first conductive pattern 15, thethird conductive pattern 19 is dominant in determining the resistance ofthe first conductive structure 22. Therefore, the resistance of thefirst conductive structure 22 is drastically decreased by the thirdconductive pattern 19 that includes a metal component. The air gap 23 isformed between the sidewalls of the third conductive pattern 19 and thesidewalls of the opening 13.

The air gap 23 may be formed as a sacrificial material is removed. Afterthe first conductive pattern 15 and the second conductive pattern 18 areformed, a sacrificial layer is formed on the sidewalls of the opening13. Subsequently, the sacrificial layer is removed after the thirdconductive pattern 19 is formed. This will be described later. A spacer14 is further formed on the sidewalls of the opening 13.

The second conductive structure 20 overlaps with a portion of the firstconductive structure 22 and caps a portion of the air gap 23. The secondconductive structure 20 may be extended to the upper surface of theinsulation layer 12. The second conductive structure 20 includes ametal-containing layer. The second conductive structure 20 may include atungsten layer.

The capping structure 24 covers the upper portion of the secondconductive structure 20 and caps the rest of the air gap 23, which isnot capped by the second conductive structure 20. The capping structure24 includes a dielectric material. The capping structure 24 includes asilicon nitride or a silicon oxide. The capping structure 24 may includea silicon nitride produced through a Plasma Enhanced Chemical VaporDeposition (PECVD) method. Since the air gap 23 has a narrow entrance,i.e., width, the air gap 23 may be capped without being filled.

A recess 21 is formed to be self-aligned to the edge of the secondconductive structure 20 and formed by recessing a portion of the firstconductive structure 22 and a portion of the air gap 23. The recess 21may be formed by recessing a portion of the insulation layer 12. Thecapping structure 24 gap-fills the recess 21.

Since the capping structure 24 is formed on the recess 21, the air gap23 is capped with a depth of the recess 21 in a subsequent process.

The air gap 23 included in the semiconductor device in accordance withthe first embodiment of the present invention is formed between thethird conductive pattern 19 and the insulation layer 12.

Referring to FIG. 1B, the air gap 23 is capped with the cappingstructure 24 and the second conductive structure 20 without the recess21.

Referring to FIG. 1C, the air gap 23 is capped with the secondconductive structure 20 and the capping structure 24. A portion of theair gap 23 is capped with the second conductive structure 20, and theother portion of the air gap 23 is capped with the capping structure 24.

In accordance with the first embodiment of the present invention and amodified example of the first embodiment, the first conductive structure22 may be a plug. The second conductive structure 20 may be a plug or aline layer. The first conductive structure 22 and the second conductivestructure 20 may form a multi-layer plug. The first conductive structure22 and the second conductive structure 20 may be a plug for coupling atransistor with a memory element. The first conductive structure 22 andthe second conductive structure 20 may be a plug for coupling atransistor with a metal line. Additionally, the first conductivestructure 22 may be a line layer, and the second conductive structure 20may be a plug. Herein, the line layer includes bit lines, metal lines,gate electrodes, word lines, or penetrating electrodes. Although notillustrated in the drawing, a third conductive structure may be furtherformed over the second conductive structure 20. The third conductivestructure may be a portion of the memory element that is electricallyconnected to the second conductive structure 20. The memory element rray include a capacitor that is formed of a storage node, a dielectriclayer, and a plate node, and the third conductive structure may includea storage node. The memory element may be realized in diverse shapes.For example, the memory element may include a variable resistivematerial. The memory element may have a stacked structure where a firstelectrode, a variable resistive material, and a second electrode aresequentially stacked, and the third conductive structure may include thefirst electrode electrically connected to the second conductivestructure 20. A data may be stored and identified depending on theresistance of the variable resistive material which is changed accordingto the voltage applied to the first electrode and the second electrode.The variable resistive material may include a phase-changing material ora magnetic tunneling junction.

FIGS. 2A to 2L are cross-sectional views describing a method forfabricating the semiconductor device in accordance with the firstembodiment of the present invention.

Referring to FIG. 2A, an insulation layer 12 is formed over a substrate11. The substrate 11 includes a semiconductor substrate. Specifically,the substrate 11 contains silicon. The substrate 11 includes a siliconsubstrate, a silicon germanium substrate, or a Silicon On Insulator(SOI) substrate. The insulation layer 12 includes a low-k dielectricmaterial. The insulation layer 12 may be a silicon nitride layer or asilicon oxide layer.

Subsequently, an opening 13 is formed in the insulation layer 12. Theopening 13 is formed to expose the surface of the substrate 11 byetching the insulation layer 12. The opening 13 may have a hole shape ora line shape. The opening 13 may be defined as a contact hole, via,through-hole, trench, or recess. An opening array may be formed, as aplurality of openings 13 are regularly disposed with a predetermined gapbetween them. A mask pattern (not shown) may be used to etch theinsulation layer 12. The mask pattern may include a photoresist patternor a hard mask pattern patterned by using the photoresist pattern.

Referring to FIG. 2B, a spacer 14 is formed on the sidewalls of eachopening 13. The spacer 14 is formed by forming an insulation layer (notshown) including the opening 13 and performing an etch-back process. Thespacer 14 includes a low-k dielectric material. The spacer 14 mayinclude a silicon nitride. As the spacer 14 is formed, the surface ofthe substrate 11 under the opening 13 is exposed. According to anotherembodiment of the present invention, the spacer 14 may be omitted.

Referring to FIG. 2C, a first conductive layer 15A is formed. The firstconductive layer 15A is formed over the insulation layer 12 includingthe spacer 14 to fill the opening 13. The first conductive layer 15Aincludes a silicidable material. The first conductive layer 15A mayinclude a silicon-containing layer. The first conductive layer 15A mayinclude polysilicon, which may be doped with an impurity. The firstconductive layer 15A is in contact with the surface of the substrate 11.

Referring to FIG. 2D, a first conductive pattern 15B is formed. Thefirst conductive layer 15A shown in FIG. 2C is recessed in the opening13 to form the first conductive pattern 15B. The first conductivepattern 15B may also be formed by performing an etch-back process on thefirst conductive layer 15A shown in FIG. 2C. The first conductivepattern 15B has a surface recessed lower than the upper surface of theinsulation layer 12. The height of the first conductive pattern 15B maybe adjusted to be as low as possible to minimize its share of the totalvolume of a conductive structure. Therefore, the resistance of theconductive structure may be decreased.

Referring to FIG. 2E, a sacrificial spacer 16 is formed. The sacrificialspacer 16 is formed on the sidewalls of the opening 13 over the firstconductive pattern 15B. The sacrificial spacer 16 may be formed byselectively etching a sacrificial layer (not shown). A dry etch processmay be used to form the sacrificial spacer 16. For example, the dry etchprocess may include an etch-back process. Through the etch process offorming the sacrificial spacer 16, the upper surface of the firstconductive pattern 15B and the upper surface of the insulation layer 12may be exposed. The sacrificial spacer 16 is removed in the subsequentprocess to form an air gap. The sacrificial spacer 16 may include amaterial having an etch selectivity to the insulation layer 12. Thesacrificial spacer 16 may include a dielectric material. The sacrificialspacer 16 may include a material different from the materials of theinsulation layer 12 and the spacer 14. For example, when the spacer 14includes a silicon nitride, the sacrificial spacer 16 may include asilicon oxide. The sacrificial spacer 16 may also be formed by stackinga silicon oxide and a silicon nitride. The deposition of a siliconnitride and an etch-back process may be performed after the uppersurface of the first conductive pattern 15B is exposed by depositing asilicon oxide and performing an etch-back process. Therefore, the spacer14 and the sacrificial spacer 16 may have a structure of NO(Nitride-Oxide) or NON (Nitride-Oxide-Nitride).

When the sacrificial spacer 16 is formed or after the sacrificial spacer16 is formed, the surface of the first conductive pattern 15B may berecessed to a predetermined depth (refer to reference numeral “15C”).This is to increase the reaction area for forming a silicide layer inthe subsequent process.

Referring to FIG. 2F, a silicidable layer 17 is formed. The silicidablelayer 17 is conformally formed over the substrate structure includingthe sacrificial spacer 16 and the first conductive pattern 15B. Thesilicidable layer 17 includes a material that forms a metal silicidethrough a silicidation reaction with the first conductive pattern 15B.The silicidable layer 17 includes a silicidable metal layer. Thesilicidable metal layer may include a metal-containing layer thatcontains a metal atom such as cobalt. When the first conductive pattern15B includes polysilicon, the silicidable layer 17 may include cobalt.The silicidable layer 17 may be deposited through a Physical VaporDeposition (PVD) process.

When the silicidable layer 17 is formed as described above, the reactionarea for forming a silicide is increased between the silicidable layer17 and the first conductive pattern 15B. For example, the increasedreaction area includes a first reaction area A1 based on the recessedsurface of the first conductive pattern 15B and a second reaction areaA2 based on a protrusion of the first conductive pattern 15B. Theincrease in the reaction area originates from the increase in the linewidth of the first conductive pattern 15B. This will be described byreferring to the following Comparative Example.

Although not illustrated in the drawing, a protective layer may beformed over the silicidable layer 17. The protective layer may beconformally formed over the silicidable layer 17. The protective layerprotects a silicide layer from being attacked in the subsequentsiliciding process. The protective layer includes a metal nitride. Theprotective layer includes a titanium-containing layer. The protectivelayer may include a titanium nitride (TiN). The protective layer may beformed by stacking titanium and a titanium nitride (Ti/TiN).

Referring to FIG. 2G, a second conductive pattern 18 is formed. Thesecond conductive pattern 18 may be formed through an annealing process18A. Through the annealing process 18A, the first conductive pattern 15Band the silicidable layer 17 react with each other to form the secondconductive pattern 18. The annealing process 18A causes a silicidationreaction. Specifically, a silicidation reaction occurs on the interfacebetween the first conductive pattern 15B and the silicidable layer 17 toform the second conductive pattern 18 including a metal silicide layer.The annealing process 18A may be performed at a temperature ofapproximately 200° C. or higher to cause the silicidation reactionbetween the first conductive pattern 15B and the silicidable layer 17.The annealing process 18A includes a Rapid Thermal Annealing (RTA)process. Through the annealing process 18A, a silicon atom of the firstconductive pattern 15B and a metal atom of the silicidable layer 17react with each other to form the second conductive pattern 18. Thesecond conductive pattern 18 may include a cobalt silicide. In thisembodiment of the present invention, the second conductive pattern 18may include a cobalt silicide of “CoSi₂ phase”. To this end, theannealing process 18A may be performed twice. For example, a primaryannealing process may be performed at a temperature of approximately400° C. to approximately 600° C. As a result of the primary annealingprocess, a cobalt silicide of “CoSi_(x) phase” (x=0.1˜1.5) is formed.Subsequently, a secondary annealing process is performed. The secondaryannealing process includes the Rapid Thermal Annealing (RTA) process.The secondary annealing process may be performed at a higher temperaturethan that of the primary annealing process. The secondary annealingprocess may be performed at a temperature of approximately 600° C. toapproximately 800° C. The secondary annealing process may be performedafter a process of removing an unreacted silicidable layer 17A isperformed. The secondary annealing process changes the phase of thesecond conductive pattern 18. For example, a cobalt silicide of“CoSi_(x) phase” (x=0.1˜1.5) is formed as a result of the primaryannealing process, and the cobalt silicide of “CoSi_(x) phase”(x=0.1˜1.5) is phase-changed into a cobalt silicide of “CoSi₂ phase”through the secondary annealing process. Among cobalt silicides, thecobalt silicide of “CoSi₂ phase” has the lowest resistivity.

After the second conductive pattern 18 is formed, there may be anunreacted silicidable layer 17A remaining. The volume of the firstconductive pattern 15B may be reduced as represented by a referencenumeral “15”.

During the annealing process 18A, since the reaction area (see A1 and A2of FIG. 2F) of silicon participating in the silicidation reaction isincreased due to the recessed surface and protrusion of the firstconductive pattern 15B, the cobalt silicide of “CoSi₂ phase” having alow resistivity may be formed. When the surface of the first conductivepattern 15B is not recessed, the reaction area of the siliconparticipating in the silicidation reaction is so insufficient that acobalt silicide of “Co₂Si phase” having a high resistivity may beformed.

As described above, when the cobalt silicide of “CoSi₂ phase” is formedfor the second conductive pattern 18, not only the contact resistance isdecreased, but also a low-resistance cobalt silicide may be formed evenin the small area of the opening 13 having a micro line width. Thesecond conductive pattern 18 functions as an ohmic contact layer betweenthe first conductive pattern 15 and a third conductive pattern.

Referring to FIG. 2H, the unreacted silicidable layer 17A s o in FIG. 2Gis removed.

Subsequently, a third conductive pattern 19A is formed over the secondconductive pattern 18. The third conductive pattern 19A is formed overthe second conductive pattern 18 to fill the opening 13. The thirdconductive pattern 19A may include a metal-containing layer. The thirdconductive pattern 19A may include a tungsten-containing material. Thethird conductive pattern 19A may include a tungsten layer or a tungstencompound layer. The third conductive pattern 19A may have the sameheight as that of the insulation layer 12. The line width of the thirdconductive pattern 19A is narrower than the first conductive pattern 15.The third conductive pattern 19A is higher than the first conductivepattern 15. Therefore, the volume of the third conductive pattern 19A isgreater than that of the first conductive pattern 15 in the conductivestructure formed in the opening 13.

As described above, a preliminary first conductive structure thatincludes the first conductive pattern 15, the second conductive pattern18, the third conductive pattern 19A, and the sacrificial spacer 16 isformed within the opening 13. A spacer 14 is formed between thesidewalls of the preliminary first conductive structure and the opening13. The sacrificial spacer 16 is formed to surround the sidewalls of thethird conductive pattern 19A.

Referring to FIG. 2I, a fourth conductive layer 20A is formed over thethird conductive pattern 19A. The fourth conductive layer 20A includes ametal-containing layer. The fourth conductive layer 20A may include atungsten-containing material. The fourth conductive layer 20A mayinclude a tungsten layer or a tungsten compound layer. The fourthconductive layer 20A may have a stacked structure including ametal-containing layer.

Referring to FIG. 2J, a fourth conductive pattern 20 is formed. Thefourth conductive pattern 20 is formed by etching the fourth conductivelayer 20A shown in FIG. 2I. A mask pattern (not shown) may be used toform the fourth conductive pattern 20. The fourth conductive pattern 20is a pattern that covers a portion of the third conductive pattern 19A.Accordingly, through the fourth conductive pattern 20, a portion of thethird conductive pattern 19A, a portion of the spacer 14, and a portionof the sacrificial spacer 16 are exposed.

Subsequently, the third conductive pattern 19A is self-aligned to theedge of the fourth conductive pattern 20 and etched to a predetermineddepth. Being self-aligned to the edge of the fourth conductive pattern20, the sacrificial spacer 16, the spacer 14 and the insulation layer 12are partially etched to a predetermined depth. As a result, a recess 21is formed. After the recess 21 is formed, the third conductive patternremains as represented by reference numeral “19.” When the recess 21 isformed, a mask pattern (not shown) may be used as an etch mask. Whenlooked on a plan view, a portion of the remaining third conductivepattern 19 is covered with the fourth conductive pattern 20, and therecess 21 exposes another portion of the remaining third conductivepattern 19.

As described above, a first conductive structure 22 is formed within theopening 13 by forming the recess 21. The first conductive structure 22includes the first conductive pattern 15, the second conductive pattern18, and the remaining third conductive pattern 19. The fourth conductivepattern 20 becomes a second conductive structure. The sacrificial spacer16 is partially etched while the recess 21 is formed. After thesacrificial spacer 16 is partially etched, the etched and exposedsacrificial spacer 16 remains as represented by a reference numeral“16A” and the sacrificial spacer 16 capped by the fourth conductivepattern 20 remains as represented by a reference numeral “16B”.

Referring to FIG. 2K, the sacrificial spacer 16 including thesacrificial spacer 16A and 16B is removed. A stripping process isperformed to remove the sacrificial spacer 16. The stripping processincludes a cleaning process. The cleaning process uses a wet chemicalcapable of removing the sacrificial spacer 16. The wet chemical removesthe sacrificial spacer 16B under the fourth conductive pattern 20. Thestripping process may include a cleaning process that is performed afterthe fourth conductive pattern 20 is etched, and in this case, thesacrificial spacer 16 is removed without an additional process.

The sacrificial spacer 16 is removed through the stripping process, andthe space that has been occupied by the sacrificial spacer 16 becomes anair gap 23.

Referring to FIGS. 1C and 2J, the sacrificial spacer 16 including thesacrificial spacer 16A and 16B is formed to surround the thirdconductive pattern 19. The fourth conductive pattern 20 caps thesacrificial spacer 16B and does not cap the sacrificial spacer 16A. Thewet chemical capable of removing the sacrificial spacer 16 graduallyflows through the fourth conductive pattern 20 into the sacrificialspacer 16B, so that the sacrificial spacer 16 including the sacrificialspacer 16A and 16B that surrounds the sidewalls of the third conductivepattern 19, is removed.

The air gap 23 exists between the sidewalls of the remaining thirdconductive pattern 19 and the sidewalls of opening 13. An insulationstructure of the air gap 23-spacer 14 is formed between the sidewalls ofthe remaining third conductive pattern 19 and the sidewalls of opening13. The second conductive pattern 18 is exposed under the air gap 23,but the first conductive pattern 15 is not exposed As described above,the air gap 23 is formed between the side ails of the remaining thirdconductive pattern 19 and the opening 13, through the stripping process.The air gap 23 is a surrounding-type gap that encloses the side wall ofthe remaining third conductive pattern 19.

Referring to FIG. 2L, a capping structure 24 is formed. The cappingstructure 24 includes a dielectric material. The capping structure 24may include a dielectric material having a low step coverage. Forexample, the capping structure 24 may be formed through a PlasmaEnhanced Chemical Vapor Deposition (PECVD) process, therefore, thecapping structure 24 may clog the entrance of the air gap 23. Thecapping structure 24 includes a silicon oxide layer or a silicon nitridelayer. The capping structure 24 may be a silicon nitride layer formedthrough the PECVD process. The capping structure 24 gap-fills the recess21 and caps the air gap 23. Also, the capping structure 24 covers theupper portion of the fourth conductive pattern 20. The capping structure24 may be formed by conformally lining a first capping layer (not shown)and then gap-filling a second capping layer (not shown)

As described above, a portion of the air gap 23 is capped with thefourth conductive pattern 20, and the other portion of the air gap 23 iscapped with the capping structure 24.

The first conductive structure 22 formed with the opening 13 includesthe first conductive pattern 15, the second conductive pattern 18, andthe remaining third conductive pattern 19. A second conductive structureincluding the fourth conductive pattern 20 is electrically connected tothe upper portion of the first conductive structure 22.

In accordance with the first embodiment of the present invention and itsmodified example, the electrical insulation characteristics of the firstconductive structure 22 are improved by forming the air gap 23. Forexample, when there is another conductive pattern adjacent to the firstconductive structure 22, parasitic capacitance between the twoconductive patterns is decreased.

Also, since the air gap 23 is formed after the second conductive pattern18 is formed, the second conductive pattern 18 may be formed in a widearea. Accordingly, interfacial resistance may be decreased.

Furthermore, since the remaining third conductive pattern 19 including ametal-containing material has a greater volume than the first conductivepattern 15 including a silicon-containing material the contactresistance of the first conductive structure 22 may be decreased.

FIG. 3A is a cross-sectional view illustrating a semiconductor device inaccordance with a second embodiment of the present invention. FIG. 3B isa cross-sectional view illustrating a semiconductor device in accordancewith a modified example of the second embodiment of the presentinvention. FIG. 3C is a plan view illustrating the semiconductor devicein accordance with the second embodiment of the present invention andthe modified example thereof.

Referring to FIG. 3A, a plurality of conductive structures are formedover a substrate 31. Each conductive structure includes a firstconductive structure 34 and a second conductive structure 46. Aninsulation structure having an air gap 45 is formed between thesidewalls of the first conductive structure 34 and the sidewalls of thesecond conductive structure 46. A spacer 35 is formed on the sidewall ofthe first conductive structure 34. The air gap 45 is formed between thespacer 35 and the sidewalls of the second conductive structure 46. Thefirst conductive structure 34 includes a first conductive pattern 32 andan insulation pattern 33. The second conductive structure 46 includes asecond conductive pattern 38, a third conductive pattern 41, and afourth conductive pattern 42. A portion of the air gap 45 is capped witha third conductive structure 43. The other portion of the air gap 45 iscapped with a capping structure 47.

The substrate 31 includes a semiconductor substrate. The substrate 31includes a silicon substrate, a silicon germanium substrate, or aSilicon On Insulator (SOI) substrate.

The first conductive structure 34 includes the first conductive pattern32. The first conductive structure 34 may have a stacked structure wherethe first conductive pattern 32 and the insulation pattern 33 arestacked. The first conductive pattern 32 may include asilicon-containing layer or a metal-containing layer. The firstconductive pattern 32 may include a silicon-containing layer and ametal-containing layer stacked therein. The first conductive pattern 32may include polysilicon, a metal, a metal nitride, and/or a metalsilicide. The first conductive pattern 32 may include a polysiliconlayer and a metal layer stacked therein. The metal layer may includetungsten.

The insulation pattern 33 includes a dielectric material. The insulationpattern 33 may include an oxide or a nitride. A hard mask pattern may bethe insulation pattern 33. The first conductive structure 34 and thesecond conductive structure 46 may have a line shape or a pillar shape.Also, one between the first conductive structure 34 and the secondconductive structure 46 may have a shape of a line stretched in onedirection. The other one may have a pillar shape. For example, the firstconductive structure 34 may be a line-shaped structure, while the secondconductive structure 46 may be a pillar-shaped structure. The firstconductive structures 34 are regularly disposed over the substrate 31with a predetermined gap between them. One between the first conductivestructure 34 and the second conductive structure 46 may be a gatestructure or a bit line structure, and the other may be a contact plug.A contact plug may include a storage node contact plug, a landing plug,and a metal contact plug. For example, the second conductive structure46 may be a contact plug, and the contact plug may have a stackedstructure of a silicon plug, an ohmic contact layer, and a metal plug.

The second conductive structure 46 includes the second conductivepattern 38 that is formed by being recessed between the neighboringfirst conductive structures 34. The second conductive structure 46 mayhave a stacked structure including the second conductive pattern 38, thethird conductive pattern 41, and the fourth conductive pattern 42. Thesecond conductive pattern 38 may include a silicon-containing layer. Thesecond conductive pattern 38 may include a polysilicon layer. The fourthconductive pattern 42 may include a metal-containing layer. The thirdconductive pattern 41 is formed between the second conductive pattern 38and the fourth conductive pattern 42. The third conductive pattern 41 isan ohmic contact layer between the second conductive pattern 38 and thefourth conductive pattern 42. The third conductive pattern 41 includes ametal silicide. The metal silicide includes a cobalt silicide. Thecobalt silicide includes a cobalt silicide of “CoSi₂ phase.”

The surface of the second conductive pattern 38 has a height recessedlower than the surface of the first conductive pattern 32. The linewidth of the fourth conductive pattern 42 is narrower than that of thesecond conductive pattern 38, and the height of the fourth conductivepattern 42 is higher than that of the second conductive pattern 38.Accordingly, the volume of the fourth conductive pattern 42 is greaterthan that of the second conductive pattern 38. An insulation structure(refer to reference numeral ‘36’ of FIG. 3C) having an opening (refer toreference numeral ‘37’ of FIG. 3C) is formed between the neighboringfirst conductive structures 34, and the second conductive structure 46may be formed within the opening 37. The opening 37 may expose thesidewalls of the neighboring first conductive structures 34.

A spacer 35 is formed on the sidewalls of the first conductive structure34. The spacer 35 includes a low-k dielectric material. The low-kdielectric material includes an oxide or a nitride. The spacer 35 mayinclude a silicon oxide, a silicon nitride, or a metal oxide.

The air gap 45 may be formed by removing a sacrificial material formedbetween the fourth conductive pattern 42 and the spacer 35.

The third conductive structure 43 overlaps with a portion of the secondconductive structure 46 while capping a portion of the air gap 45. Thethird conductive structure 43 may be extended to the upper surface ofthe first conductive structure 34. The third conductive structure 43includes a metal-containing layer. The third conductive structure 43 mayinclude a tungsten layer.

The capping structure 47 covers the upper portion of the thirdconductive structure 43 while capping the other portion of the air gap45. The capping structure 47 includes a dielectric material. The cappingstructure 47 includes a silicon nitride or a silicon oxide. The cappingstructure 47 may include a silicon nitride deposited through a PlasmaEnhanced Chemical Vapor Deposition (PECVD) process.

A recess 44 is formed by being self-aligned to the edge of the thirdconductive structure 43 and recessing a portion of the second conductivestructure 46 and a portion of the air gap 45. The recess 44 may also beformed by recessing a portion of the first conductive structure 34. Thecapping structure 47 is formed in the recess 44.

Referring to FIG. 3B, the air gap 45 is capped with the cappingstructure 47 and the third conductive structure 43 without the recess 4.

Referring to FIG. 3C, the air gap 45 is capped with the third conductivestructure 43 and the capping structure 47. A portion of the air gap 45is capped with the third conductive structure 43, and the other portionof the air gap 45 is capped with the capping structure 47. The air gap45 is formed between the first conductive structure 34 and the fourthconductive pattern 42. An insulation structure 36 is formed between theneighboring first conductive structures 34. The opening 37 is formed inthe insulation structure 36. The second conductive structure 46 isformed within the opening 37. The spacer 35 is formed on the sidewallsof the opening 37.

In accordance with the second embodiment of the present invention andits modified example, the air gap 45 is stably capped with the thirdconductive structure 43 and the capping structure 47. With the air gap45, the parasitic capacitance between the first conductive structure 34and the second conductive structure 46 is decreased.

The air gap 45 may be formed after the third conductive pattern 41 andthe fourth conductive pattern 42 are formed over the second conductivepattern 38. As a result, the area where the third conductive pattern 41is to be formed may be secured to be wide. The resistance of the secondconductive structure 46 may be reduced by minimizing the volume of thesecond conductive pattern 38, which is a silicon-containing layer, andmaximizing the volume of the fourth conductive pattern 42, which is ametal-containing layer. Moreover, with the third conductive pattern 41,which is an ohmic contact layer, the resistance is decreased even more,and since the third conductive pattern 41 is formed in a wide area,interface resistance is decreased.

The second conductive structure 46 in accordance with the secondembodiment of the present invention and its modified example may be aplug. The third conductive structure 43 may be a plug or a line layer.The second conductive structure 46 and the third conductive structure 43may be a multi-layer plug. For example, the second conductive structure46 may be a first plug structure, and the third conductive structure 43may be a second plug structure. The second conductive structure 46 has astructure where a silicon plug, an ohmic contact layer, and a metal plugare stacked, and the air gap 45 may be formed on the sidewalls of themetal plug. The second conductive structure 46 and the third conductivestructure 43 may be a plug for coupling a transistor with a memoryelement. The second conductive structure 46 and the third conductivestructure 43 may be a plug for coupling a transistor with a metal line.Additionally, the second conductive structure 46 may be a line layer,and the third conductive structure 43 may be a plug. Herein, the linelayer includes bit lines, metal lines, gate electrodes, word lines, orthrough silicon vias. Although not illustrated in the drawing, a fourthconductive structure may be further formed over the third conductivestructure 43. The fourth conductive structure may be a portion of amemory element that is electrically connected to the third conductivestructure 43. The memory element may include a capacitor formed of astorage node, a dielectric layer, and a plate node, and the fourthconductive structure may include a storage node. The memory element maybe realized in diverse forms. For example, the memory element mayinclude a variable resistive material. The memory element may be formedby sequentially stacking a first electrode, a variable resistivematerial, and a second electrode, and the fourth conductive structuremay include the first electrode electrically connected to the thirdconductive structure 43. A data may be stored and identified dependingon the resistance of the variable resistive material which is changedaccording to the voltage applied to the first electrode and the secondelectrode. The variable resistive material may include a phase-changematerial or a magnetic tunneling junction.

FIGS. 4A to 4K are cross-sectional views describing a method forfabricating the semiconductor device in accordance with the secondembodiment of the present invention.

Referring to FIG. 4A, a plurality of first conductive structures 34 areformed over a substrate 31. The substrate 31 includes a semiconductorsubstrate. The substrate 31 contains silicon. The substrate 31 mayinclude a silicon substrate or a silicon germanium substrate. Also, thesubstrate 31 may include a Silicon On Insulator (SOI) substrate.

The first conductive structures 34 formed over the substrate 31 areregularly disposed with a predetermined gap between them. A hard maskpattern 33 is formed over a first conductive layer (not shown) to formthe first conductive structures 34. A first conductive pattern 32 isformed by using the hard mask pattern 33 as an etch mask and etching thefirst conductive layer (not shown). A first conductive structure 34where the first conductive pattern 32 and the hard mask pattern 33 arestacked is formed. The first conductive pattern 32 includes asilicon-containing layer or a metal-containing layer. For example, thefirst conductive pattern 32 may include polysilicon or tungsten. Also,the first conductive pattern 32 is formed by stacking asilicon-containing layer and a metal-containing layer. For example, thefirst conductive pattern 32 may be formed by stacking a polysiliconlayer and a tungsten layer. A barrier layer may be further formedbetween the polysilicon layer and the tungsten layer. The firstconductive pattern 32 may be a stacked structure including a polysiliconlayer, a titanium-containing layer, and a tungsten layer. Thetitanium-containing layer is a barrier layer, and titanium (Ti) and atitanium nitride (TiN) may be stacked. The hard mask pattern 33 isformed of a dielectric material.

A first insulation layer 35A is formed over the multiple firstconductive structures 34. The first insulation layer 35A includes alow-k dielectric material. The first insulation layer 35A includes anitride or an oxide. For example, the first insulation layer 35A mayinclude a silicon nitride or a silicon oxide. The first insulation layer35A is conformally formed over the substrate structure including thefirst conductive structures 34. The first insulation layer 35A is amaterial that later becomes a spacer.

A second insulation layer 36A is formed over the first insulation layer35A. The second insulation layer 36A may include a silicon oxide. Thesecond insulation layer 36A may be formed over the first insulationlayer 35A to fill the space between the first conductive structures 34.The second insulation layer 36A becomes an insulation layer 36.

Referring to FIG. 4B, the second insulation layer 36A is planarized. Thesecond insulation layer 36A may be planarized to expose the surface ofthe first insulation layer 35A over the first conductive structures 34.

Openings 37 are formed by etching the second insulation layer 36A. Theinsulation layer 36 obtained after the openings 37 are formed is notshown in the cross-sectional view. A mask pattern (not shown) may beused to form the openings 37. The openings 37 may have a hole shape or aline shape. The openings 37 may be formed between the first conductivestructures 34. The first insulation layer 35A may be exposed on thesidewalls of each opening 37. To form the openings 37, the secondinsulation layer 36A may be etched to be aligned to the first conductivestructures 34 and the first insulation layer 35A.

The first insulation layer 35A may remain over the substrate 31 underthe openings 37.

Subsequently, the surface of the substrate 31 is exposed by etching thefirst insulation layer 35A. Since the first insulation layer 35A isetched, a spacer 35 is formed on the sidewalls of each first conductivestructure 34.

According to another embodiment of the present invention, the spacers 35are formed after the openings 37 are formed. That is, after the openings37 are formed, the first insulation layer 35A is formed over the firstconductive structures 34 and the insulation layer 36. The spacers 35 areformed by etching the first insulation layer 35A. According to yetanother embodiment of the present invention, the spacers 35 may beomitted.

Referring to FIG. 4C, a second conductive pattern 38A is formed. Asecond conductive layer (not shown) filling the openings 37 is formedover the substrate structure including the spacers 35. The secondconductive layer (not shown) is etched through an etch-back process. Asa result, the second conductive pattern 38A recessed in the openings 37is formed. The second conductive pattern 38A has its recessed surfacelower than the upper surface of the first conductive structures 34. Thesecond conductive pattern 38A includes a silicidable material. Thesecond conductive pattern 38A may include a silicon-containing layer.The second conductive pattern 38A may include polysilicon. Thepolysilicon may be doped with an impurity. The second conductive pattern38A is in contact with the surface of the substrate 31. The height ofthe second conductive pattern 38A may be controlled to be as low aspossible. This is to minimize the share of the second conductive pattern38A in the total volume of a second conductive structure.

Referring to FIG. 4D, sacrificial spacers 39 are formed. Eachsacrificial spacer 39 is formed on the sidewall of each opening 37 overthe second conductive pattern 38A. The sacrificial spacers 39 may beformed by selectively etching a sacrificial layer (not shown). A dryetch process may be performed to form the sacrificial spacers 39. Forexample, the dry etch process may include an etch-back process. Throughthe etch process of forming the sacrificial spacers 39, the uppersurface of the second conductive pattern 38A is exposed. The sacrificialspacers 39 are removed in the subsequent process to form air gaps. Thesacrificial spacers 39 may include a dielectric material, and thesacrificial spacers 39 may include a silicon oxide or a silicon nitride.The sacrificial spacers 39 may be formed by stacking a silicon oxide anda silicon nitride.

When the sacrificial spacers 39 are formed or after the sacrificialspacers 39 are formed, the surface of the second conductive pattern 38Amay be recessed to a predetermined depth (refer to reference numeral‘38C’). The recessed second conductive pattern is denoted as a referencenumeral ‘38B’. The second conductive pattern 38A is recessed to widenthe reaction area for forming a silicide layer later.

Referring to FIG. 4E, a silicidable layer 40 is formed. The silicidablelayer 40 is conformally formed over the substrate structure includingthe sacrificial spacers 39 and the recessed second conductive pattern38B. The silicidable layer 40 includes a material that forms a metalsilicide through a silicidation reaction with the recessed secondconductive pattern 38B. The silicidable layer 40 includes a silicidablemetal layer. The silicidable metal layer may include a metal-containinglayer that contains a metal atom such as cobalt. When the recessedsecond conductive pattern 38B includes polysilicon, the silicidablelayer 40 may include cobalt. The silicidable layer 40 may be depositedthrough a Physical Vapor Deposition (PVD) process.

When the silicidable layer 40 is formed as described above, the reactionarea for forming a silicide is increased between the silicidable layer40 and the recessed second conductive pattern 38B. For example, theincreased reaction area includes a first reaction area A1 based on therecessed surface of the recessed second conductive pattern 38B and asecond reaction area A2 based on a protrusion of the recessed secondconductive pattern 38B. The increase in the reaction area originatesfrom the increase in the line width of the recessed second conductivepattern 38B. This will be described by referring to the followingcomparative example.

Although not illustrated in the drawing, a protective layer may beformed over the silicidable layer 40. The protective layer may beconformally formed over the silicidable layer 40. The protective layerprotects a silicide layer from being attacked in the subsequentsiliciding process. The protective layer includes a metal nitride. Theprotective layer includes a titanium-containing layer. The protectivelayer may include a titanium nitride (TiN). The protective layer may beformed by stacking titanium and a titanium nitride (Ti/TiN).

Referring to FIG. 4F, a third conductive pattern 41 is formed. The thirdconductive pattern 41 may be formed through an annealing process 41A.Through the annealing process 41A, the recessed second conductivepattern 38B and the silicidable layer 40 react with each other to formthe third conductive pattern 41. The annealing process 41A causes asilicidation reaction. Specifically, a silicidation reaction occurs onthe interface between the recessed second conductive pattern 38B and thesilicidable layer 40 to form the third conductive pattern 41 including ametal silicide layer. The annealing process 41A may be performed at atemperature of approximately 200° C. or higher to cause the silicidationreaction between the silicidable layer 40 and the recessed secondconductive pattern 38B. The annealing process 41A includes a RapidThermal Annealing (RTA) process. Through the annealing process 41A, asilicon atom of the recessed second conductive pattern 38B and a metalatom of the silicidable layer 40 react with each other to form the thirdconductive pattern 41. The third conductive pattern 41 may include acobalt silicide. In this embodiment of the present invention, the thirdconductive pattern 41 may include a cobalt silicide of “CoSi₂ phase.” Tothis end, the annealing process 41A may be performed twice. For example,a primary annealing process may be performed at a temperature ofapproximately 400° C. to approximately 600° C. As a result of theprimary annealing process, a cobalt silicide of “CoSi_(x) phase”(x=0.1˜1.5) is formed. Subsequently, a secondary annealing process isperformed. The secondary annealing process includes the Rapid ThermalAnnealing (RTA) process. The secondary annealing process may beperformed at a higher temperature than that of the primary annealingprocess. The secondary annealing process may be performed at atemperature of approximately 600° C. to approximately 800° C. Thesecondary annealing process changes the phase of the third conductivepattern 41. For example, a cobalt silicide of “CoSi_(x) phase”(x=0.1˜1.5) is formed as a result of the primary annealing process, andthe cobalt silicide of “CoSi_(x) phase” (x=0.1˜1.5) is phase-changedinto a cobalt silicide of “CoSi₂ phase” through the secondary annealingprocess. Among cobalt silicides, the cobalt silicide of “CoSi₂ phase”has the lowest resistivity.

After the third conductive pattern 41 is formed, there may be anunreacted silicidable layer 40A remaining. The volume of the recessedsecond conductive pattern 38B may be reduced as represented by areference numeral “38.”

During the annealing process 41A, since the reaction area (see A1 and A2of FIG. 4E) of silicon participating in the silicidation reaction isincreased due to the recessed surface and protrusion of the recessedsecond conductive pattern 38B, the cobalt silicide of “CoSi₂ phase”having a low resistivity may be formed. When the surface of the recessedsecond conductive pattern 38B is not recessed, the reaction area of thesilicon participating in the silicidation reaction is so insufficientthat a cobalt silicide of “Co₂Si phase” having a high resistivity may beformed.

As described above, when the cobalt silicide of “CoSi₂ phase” is formedfor the third conductive pattern 41, not only the contact resistance isdecreased, but also a low-resistance cobalt silicide may be formed evenin the small area of the openings 37 having a micro line width. Thethird conductive pattern 41 functions as an ohmic contact layer.

Referring to FIG. 4G, the unreacted silicidable layer 40A shown in FIG.4F is removed.

Subsequently, a fourth conductive pattern 42 is formed over the thirdconductive pattern 41 to fill the openings 37. The fourth conductivepattern 42 may include a metal-containing layer. The fourth conductivepattern 42 may include a tungsten-containing material. The fourthconductive pattern 42 may include a tungsten layer or a tungstencompound layer.

The height of the fourth conductive pattern 42 may be higher than thatof the second conductive pattern 38. The line width of the fourthconductive pattern 42 is narrower than the second conductive pattern 38.Therefore, the volume of the fourth conductive pattern 42 is greaterthan that of the second conductive pattern 38.

As described above, when the fourth conductive pattern 42 is formed, apreliminary second conductive structure is formed within the openings37. The preliminary second conductive structure includes the secondconductive pattern 38, the third conductive pattern 41, the fourthconductive pattern 42, and the sacrificial spacers 39. The sacrificialspacers 39 may have a surrounding form that encloses the sidewalls ofthe fourth conductive pattern 42.

Referring to FIG. 4H, a fifth conductive layer 43A is formed over thefourth conductive pattern 42. The fifth conductive layer 43A includes ametal-containing layer. The fifth conductive layer 43A may include atungsten-containing material. The fifth conductive layer 43A may includea tungsten layer or a tungsten compound layer.

Referring to FIG. 4I, third conductive structures 43 are formed. Thethird conductive structures 43 are formed by etching the fifthconductive layer 43A shown in FIG. 4H. A mask pattern (not shown) may beused to form the third conductive structures 43. The third conductivestructures 43 are a pattern that covers a portion of the fourthconductive pattern 42. Accordingly, through each third conductivestructure 43, a portion of the fourth conductive pattern 42, a portionof each spacer 35, and a portion of each sacrificial spacer 39 areexposed.

Subsequently, recesses 44 are formed. The fourth conductive pattern 42exposed through the third conductive structures 43 is etched to apredetermined depth and a portion of the sacrificial spacer 39, aportion of the spacer 35, and a portion of the hard mask pattern 33 areetched to a predetermined depth.

Referring to FIG. 4J, air gaps 45 are formed by removing the sacrificialspacers 39. Each air gap 45 is formed between the sidewall of the fourthconductive pattern 42 and the sidewall of each first conductivestructure 34. The sacrificial spacers 39 may be removed through a wetetch process. A cleaning process using a wet chemical may be performedto remove the sacrificial spacers 39. The cleaning process may include acleaning process that is performed after the third conductive structures43 are etched. In this manner, the sacrificial spacers 39 may be removedwithout an additional process.

The sacrificial spacers 39 are removed through the above-describedprocess, and the space occupied by the sacrificial spacers 39 remains asthe air gaps 45.

The air gaps 45 are formed between the sidewalls of the fourthconductive pattern 42 and the sidewalls of each first conductivestructure 34. An insulation structure of “air gap 45-spacer 35” isformed between the sidewalls of the fourth conductive pattern 42 and thesidewalls of each first conductive structure 34. The third conductivepattern 41 is exposed under the air gaps 45, but the second conductivepattern 38 is not exposed.

The air gaps 45 may be surrounding-type gaps each of which encloses thesidewalls of the fourth conductive pattern 42. Second conductivestructures 46 are formed within the openings by the recesses 44. Eachsecond conductive structure 46 includes the second conductive pattern38, the third conductive pattern 41, and the fourth conductive pattern42.

Referring to FIG. 4K, capping structures 47 are formed. The cappingstructures 47 include a dielectric material. The capping structures 47may include a dielectric material having a low step coverage. Forexample, the capping structures 47 may be formed through a PlasmaEnhanced Chemical Vapor Deposition (PECVD) process, therefore, thecapping structures 47 may clog the entrances of the air gaps 45. Thecapping structures 47 include a silicon oxide layer or a silicon nitridelayer. The capping structures 47 may be a silicon nitride layer formedthrough the PECVD process.

The capping structures 47 gap-fill the recesses 44 while capping the airgaps 45. Additionally, the capping structures 47 cover the upperportions of the third conductive structures 43. The capping structures47 may be formed by conformally lining a first capping layer thengap-filling a second capping layer.

As described above, a portion of each air gap 45 is capped with a thirdconductive structure 43, and the other portion of the air gap 45 iscapped with the capping structure 47.

The second conductive structures 46 formed within the openings 37include the second conductive pattern 38, third conductive pattern 41,and the fourth conductive pattern 42. The third conductive structures 43are electrically connected to the upper portions of the secondconductive structures 46.

FIGS. 5A to 5D are cross-sectional views illustrating a comparativeexample of the second embodiment of the present invention.

Referring to FIG. 5A, a plurality of first conductive structures 34where a first conductive pattern 32 and a hard mask pattern 33 arestacked are formed over a substrate 31.

Subsequently, openings are formed between the first conductivestructures 34, and spacers 35 are formed on the sidewalls of the firstconductive structures 34.

Subsequently, recessed second conductive pattern 38 and recessedsacrificial spacers 39 are formed.

Referring to FIG. 5B, air gaps 45 are formed by removing the sacrificialspacers 39 shown in FIG. 5A.

Referring to FIG. 5C, capping spacers 43A for capping the air gaps 45are formed.

Referring to FIG. 5D, a third conductive pattern 41B and a fourthconductive pattern 42A are formed over the second conductive pattern 38.

According to the comparative example, the sacrificial spacers 39 may beformed of silicon oxide silicon nitride, or titanium nitride. The airgaps 45 are formed by removing the sacrificial spacers 39 through a wetetch process.

According to the comparative example, when the sacrificial spacers 39are formed of titanium nitride, it is difficult to entirely remove thetitanium nitride, causing a Not-Open phenomenon of the air gaps 45.Also, when the titanium nitride is removed, the neighboring structuresmay be damaged.

Also, according to the comparative example, when the capping spacers 43Aare thick to sufficiently cap the air gaps 45, the space (refer to “W”of FIG. 5C) where the fourth conductive pattern 42A is formed and thearea where the third conductive pattern 41B is formed become small sothat the contact resistance is increased. Since the line width of thesecond conductive pattern 38 is decreased as much as the space of theair gaps 45 according to the comparative example, the area where thethird conductive pattern 41B is formed is decreased.

Additionally, according to the comparative example, when the cappingspacers 43A are thin, the air gaps 45 may be open during the formationof the capping spacers 43A. Also, the capping spacers 43A may be lostexposing the air gaps 45 during a stripping process and a cleaningprocess that are accompanied in the subsequent process of forming thethird conductive pattern 41B. As a result, the fourth conductive pattern42A flows into the air gaps 45 to fill the air gaps 45.

According to the comparative example, resistance is increased due to thevolume of the second conductive pattern 38 including asilicon-containing layer being relatively greater than that of thefourth conductive pattern 42A including a metal-containing layer.Therefore, there is a limitation in decreasing the resistance of contactplugs.

As described in the embodiments of the present invention, the volume ofthe metal-containing layer is greater than that of a silicon-containinglayer. Therefore, the resistance may be decreased. Since the air gaps 45are formed after the third conductive pattern 41 is formed, the areawhere the third conductive pattern 41 is formed is increased. Therefore,the contact resistance may be decreased. Moreover, since the strippingprocess and the cleaning process that are performed after the thirdconductive pattern 41 is formed, are performed prior to the process offorming the air gaps 45, the loss of the air gaps 45 is minimized. Sincethe air gaps 45 are capped with the third conductive structures 43 andcapping structures 47 shown in FIG. 4K, the air gaps 45 may be cappedstably. Also, the fabrication process may be simplified because theformation of capping spacers including a dielectric material is omitted.The fabrication process is even more simplified because the sacrificialspacers 39 are removed in the cleaning process that is performed afterthe third conductive structures 43 are formed. Since the air gaps 45 areformed after the third conductive structures 43 are formed, the air gaps45 are not exposed during the etch process of the third conductivestructures 43.

FIG. 6A is a cross-sectional view illustrating a portion of a memorycell. FIG. 6B is a plan view illustrating the memory cell of FIG. 6A.FIG. 6C is a cross-sectional view illustrating the memory cell takenalong a line B-B′ of FIG. 6B. The memory cell shown in FIG. 6A includesa Dynamic Random Access Memory (DRAM) memory cell.

Referring to FIGS. 6A, 6B and 6C, active regions 303 are defined in asubstrate 301 by isolation regions 302. Gate trenches 322 traversing theactive regions 303 are formed. A gate insulation layer 323 is formed onthe surface of the gate trenches 322. Buried gate electrodes 324partially filling the gate trenches 322 are formed over the gateinsulation layer 323. Although not illustrated, a source region and adrain region are formed in the substrate 301. A sealing layer 325 isformed over the buried gate electrodes 324. Bit line structures 310including bit lines 307 that are stretched in a direction crossing theburied gate electrodes 324 are formed over the substrate 301.

The bit line structures 310 include the bit lines 307, a bit line hardmask 308, and bit line spacers 309. The bit lines 307 are coupled withthe active regions 303 through bit line contact plugs 306. The bit linecontact plugs 306 are formed in bit line contact holes 305 that areformed in a first inter-layer dielectric layer 304.

Storage node contact plugs are formed to be coupled with the activeregions 303. The storage node contact plugs include first contact plugs312 and second contact plugs 319. The first contact plugs 312 are formedin contact holes 311 to penetrate through the first inter-layerdielectric layer 304 and a second inter-layer dielectric layer 304A.Spacers 317 are formed on the sidewalls of the contact holes 311. Eachfirst contact plug 312 includes a first plug 313, an ohmic contact layer314, and a second plug 315. The first plug 313 is a silicon plugincluding polysilicon. The second plug 315 is a metal plug includingtungsten. The ohmic contact layer 314 includes a metal silicide. Theohmic contact layer 314 includes a cobalt suicide of “CoSi₂ phase.” Thefirst contact plugs 312 have a semi-metal plug structure. The firstplugs 313 are recessed to have a surface lower than the bottom surfaceof the bit lines 307. Each second contact plug 319 caps a portion ofeach air gap 316 and the second plug 315 of each first contact plug 312.The other portion of the air gap 316 is capped with a capping structure320. The capping structures 320 gap-fill recesses 318.

An insulation structure including the air gap 316 and the spacer 317 isformed between each first contact plug 312 and each bit line 307. Theair gap 316 spaces out the second plug 315 from the sidewall of the bitline 307.

A capacitor including a storage node 321 is coupled with the upperportion of each second contact plug 319. The storage node 321 includes apillar shape. Although not illustrated in the drawing, a dielectriclayer and a plate node may be further formed over the storage node 321.The storage node 321 may also have a cylindrical shape other than thepillar shape.

As described above, the memory cell includes the buried gate-typetransistor including the buried gate electrodes 324, the bit lines 307,and the capacitor. Each of the first contact plugs 312 is spaced out bythe air gap 316 from the sidewall of the bit line 307. The parasiticcapacitance between the bit line 307 and the first contact plug 312 isgenerated between the second plug 315 and the bit line 307. The totalresistance of the first contact plug 312 is decreased by the second plug315 including a metal-containing material. The air gaps 316 decrease theparasitic capacitance between the bit lines 307 and the first contactplugs 312.

FIGS. 7A to 7L are cross-sectional views exemplarily describing a methodfor fabricating a memory cell.

Referring to FIG. 7A, a substrate 51 includes silicon. The substrate 51may include a silicon substrate or a silicon germanium substrate. Also,the substrate 51 may include a Silicon On Insulator (SOI) substrate.

Isolation regions 52 are formed in the substrate 51. The isolationregions 52 may be formed through a Shallow Trench Isolation (STI)process. The isolation regions 52 define active regions 53. Theisolation regions 52 may be formed by sequentially forming a wall oxide,a liner, and a gap-fill material. The liner may include a siliconnitride or a silicon oxide. The silicon nitride may include Si₃N₄, andthe silicon oxide may include SiO₂. The gap-fill material may include asilicon oxide such as a Spin-On-Dielectric (SOD) material. Also, thegap-fill material may include a silicon nitride. Herein, the siliconnitride may be the same material of the liner.

Although not illustrated in the drawing, after the isolation regions 52are formed, buried gate electrodes (refer to ‘324’ of FIG. 6C) may beformed. Hereafter, a method for forming the buried gate electrodes isdescribed with reference to FIG. 6C. After the gate trenches 322 areformed by etching the substrate 301, the buried gate electrodes 324recessed in the gate trenches 322 are formed. Subsequently, a sealinglayer 325 is formed over the buried gate electrodes 324. Before theburied gate electrodes 324 are formed, the gate insulation layer 323 maybe formed on the surface of the gate trenches 322. The buried gateelectrodes 324 may be formed by forming a metal-containing layer togap-fill the gate trenches 322 then performing an etch-back process. Themetal-containing layer may include a material including a metal as amain component, such as titanium, tantalum, or tungsten. Themetal-containing layer may include at least one selected from the groupconsisting of tantalum nitride (TaN), titanium nitride (TiN), tungstennitride (WN), and tungsten (W). For example, the buried gate electrodes324 may include tantalum nitride (TaN), titanium nitride (TiN), ortungsten (W) alone, or the buried gate electrodes 324 may be formed in adouble layer structure of TiN/W or TaN/W where tungsten (W) is stackedover titanium nitride (TiN) or tantalum nitride (TaN). Also, the buriedgate electrodes 324 may be formed in a double layer structure of WN/Wwhere tungsten (W) is stacked over tungsten nitride (WN). Additionally,the buried gate electrodes 324 may include a metal material having a lowresistance. The sealing layer 325 may gap-fill the gate trenches 322over the buried gate electrodes 324. The sealing layer 325 may alsoprotect the buried gate electrodes 324 from the subsequent process. Thesealing layer 325 may include a dielectric material. The sealing layer325 may include a silicon nitride. After the formation of the sealinglayer 325, a source region and a drain region may be formed in eachactive region 303. As a result, the buried gate-type transistorincluding the buried gate electrodes 324 is formed.

Referring to FIG. 7A, a first inter-layer dielectric layer 54 is formedover the substrate 51. The first inter-layer dielectric layer 54 mayinclude a silicon oxide or a silicon nitride. The first inter-layerdielectric layer 54 functions as an inter-layer dielectric layer. Anetch-stop layer (not shown) including a silicon nitride may be furtherformed over the first inter-layer dielectric layer 54.

Bit line contact holes 55 are formed by etching the first inter-layerdielectric layer 54. The bit line contact holes 55 may be formed using amask pattern (not shown) as an etch mask. After the bit line contactholes 55 are formed, the active regions 53 may be recessed to apredetermined depth. As a result, the contact area may be increasedbetween the active region 53 and a bit line contact plug 56 that isformed in each bit line contact hole 55. The active region 53 exposedthrough each bit line contact hole 55 includes one region between thesource region and the drain region of the buried gate-type transistor.

The bit line contact plugs 56 are formed in the bit line contact holes55. The bit line contact plugs 56 fill the bit line contact holes 55. Aconductive layer (not shown) is formed over the substrate structure togap-fill the bit line contact holes 55 then the conductive layer (notshown) is planarized. As a result, the bit line contact plugs 56 areformed. The bit line contact plugs 56 may include a polysilicon layer ora metal layer.

Bit lines 57 and a bit line hard mask 58 are formed over the bit linecontact plugs 56. According to another embodiment of the presentinvention, the line widths of the bit lines 57 and the bit line hardmask 58 are set to be shorter than the bit line contact holes 55 so asto etch the bit line contact plugs 56. As the bit line contact plugs 56are etched, the sidewalls of the bit line contact holes 55 may beexposed again, but the exposed sidewalls of the bit line contact holes55 may be gap-filled with bit line spacers 59, are to be formedsubsequently. The bit lines 57 include a metal-containing layercontaining a metal such as tungsten. The bit line hard mask 58 includesa silicon nitride.

The bit line spacers 59 are formed on the sidewalls of the bit line hardmask 58. The bit line spacers 59 may include a silicon nitride.

As described above, if the bit line spacers 59 are formed, bit linestructures 60 including the bit lines 57, the bit line hard mask 58 andthe bit line spacers 59 are formed. Although not illustrated in thedrawing, when the bit line structures 60 are formed, a gate structure ofthe transistor may be simultaneously formed in a peripheral circuitregion. The gate structure of the transistor formed in the peripheralcircuit region may include a buried gate type, a planar gate type, or arecess gate type.

A second inter-layer dielectric layer 61 is formed over the bit linestructures 60. Subsequently, the second inter-layer dielectric layer 61may be patterned or planarized to gap-fill the space between theneighboring bit line structures 60.

Referring to FIG. 7B, the second inter-layer dielectric layer 61 shownin FIG. 7A and the first inter-layer dielectric layer 54 are etchedusing the mask pattern (not shown) as an etch mask. As a result, contactholes 62 are formed between the bit line structures 60. The contactholes 62 may be formed to be self-aligned by the bit line structures 60.As a result, the contact holes 62 expose the sidewalls of theneighboring bit line structures 60. Each contact hole 62 exposes aportion of the surface of the substrate 51. Each active region 53exposed through the contact holes 62 includes one region between thesource region and the drain region of the buried gate-type transistor.Although not illustrated in the drawing, the lower portion of eachcontact hole 62 may be widened by performing a subsequent wet etchprocess. Herein, a portion of the first inter-layer dielectric layer 54is etched.

Referring to FIG. 7C, spacers 63 are formed on the sidewalls of thecontact holes 62. Specifically, the spacers 63 are formed by forming aninsulation layer (not shown) then performing an etch-back process on theinsulation layer (not shown). The spacers 63 are formed on the sidewallsof the contact holes 62. As a result of the formation of the spacers 63,the surface of the active regions 53 under the contact holes 62 isexposed. According to another embodiment of the present invention, theformation of the spacers 63 may be omitted.

Referring to FIG. 7D, first plugs 64A are formed in the contact holes62. Each of the first plugs 64A fills a portion of each contact hole 62.That is, the first plugs 64A are formed to be recessed in the contactholes 62. The first plugs 64A are formed by forming a conductive layer(not shown) over the substrate structure to gap-fill the contact holes62 and recessing the conductive layer. The recessed surface of the firstplugs 64A may be controlled to be lower than at least the bottom surfaceof the bit lines 57. Accordingly, the bit lines 57 and the first plugs64A do not confront with each other. The first plugs 64A include asilicon-containing layer. The first plugs 64A may include a polysiliconlayer. The first plugs 64A may be silicon plugs.

Referring to FIG. 7E, sacrificial spacers 65 are formed on the sidewallsof the contact holes 62 in the upper portion of the first plugs 64A. Thesacrificial spacers 65 may be formed by selectively etching asacrificial layer (not shown). The sacrificial spacers 65 may be formedthrough a dry etch process. For example, the dry etch process mayinclude an etch-back process. Through the etch process of forming thesacrificial spacers 65, the upper surface of the first plugs 64A isexposed. The sacrificial spacers 65 are removed in the subsequentprocess to form air gaps. The sacrificial spacers 65 may include adielectric material, and the sacrificial spacers 65 may include asilicon oxide or a silicon nitride. The sacrificial spacers 65 may beformed by stacking a silicon oxide or a silicon nitride.

When the sacrificial spacers 65 are formed or after the sacrificialspacers 65 are formed, the surface of the first plugs 64A may berecessed to a predetermined depth (refer to a reference numeral “64C.”The recessed first plugs 64A are denoted as “64B.” This is to increasethe reaction area for forming a silicide layer in the subsequentprocess.

Referring to FIG. 7F, a silicidable layer 66 is formed. The silicidablelayer 66 is conformally formed over the substrate structure includingthe sacrificial spacers 65 and the recessed first plugs 64B. Thesilicidable layer 66 includes a material that forms a metal silicidethrough a silicidation reaction with the recessed first plugs 64B. Thesilicidable layer 66 includes a silicidable metal layer. The silicidablemetal layer may include a metal-containing layer including a metal atomsuch as cobalt. When the recessed first plugs 64B include polysilicon,the silicidable layer 66 may include cobalt. The silicidable layer 66may be deposited through a Physical Vaper Deposition (PVD) process.

When the silicidable layer 66 is formed as described above, the reactionarea for forming a silicide is increased between the silicidable layer66 and the recessed first plugs 64B. For example, the increased reactionarea includes a first reaction area based on the recessed surface of therecessed first plugs 64B and a second reaction area based on aprotrusion of the recessed first plugs 64B. The increase in the reactionarea originates from the increase in the line width of the recessedfirst plugs 64B.

Although not illustrated in the drawing, a protective layer may beformed over the silicidable layer 66. The protective layer may beconformally formed over the silicidable layer 66. The protective layerprotects a silicide layer from being attacked in the subsequentshielding process. The protective layer includes a metal nitride. Theprotective layer includes a titanium-containing layer. The protectivelayer may include a titanium nitride (TiN). The protective layer may beformed by stacking titanium and a titanium nitride (Ti/TiN).

Referring to FIG. 7G, an ohmic contact layer 67 is formed. The ohmiccontact layer 67 may be formed through an annealing process 67A. Throughthe annealing process 67A, the recessed first plugs 64B and thesilicidable layer 66 react with each other to form the ohmic contactlayer 67. The annealing process 67A causes a silicidation reaction.Specifically, a silicidation reaction occurs on the interface betweenthe recessed first plugs 64B and the silicidable layer 66 to form theohmic contact layer 67 including a metal silicide layer. The annealingprocess 67A may be performed at a temperature of approximately 200° C.or higher to cause the silicidation reaction between the silicidablelayer 66 and the recessed first plugs 64B. The annealing process 67Aincludes a Rapid Thermal Annealing (RTA) process. Through the annealingprocess 67A, a silicon atom of the recessed first plugs 64B and a metalatom of the silicidable layer 66 react with each other to form the ohmiccontact layer 67. The ohmic contact layer 67 may include a cobaltsilicide. In this embodiment of the present invention, the ohmic contactlayer 67 may include a cobalt silicide of “CoSi₂ phase.” To this end,the annealing process 67A may be performed twice. For example, a primaryannealing process may be performed at a temperature of approximately400° C. to approximately 600° C. As a result of the primary annealingprocess a cobalt silicide of “CoSi_(x) phase” (x=0.1˜1.5) is formed.Subsequently, a secondary annealing process is performed. The secondaryannealing process includes the Rapid Thermal Annealing (RTA) process.The secondary annealing process may be performed at a higher temperaturethan that of the primary annealing process. The secondary annealingprocess may be performed at a temperature of approximately 600° C. toapproximately 800° C. The secondary annealing process changes the phaseof the ohmic contact layer 67. For example, a cobalt silicide of“CoSi_(x) phase” (x=0.1˜1.5) is formed as a result of the primaryannealing process, and the cobalt silicide of “CoSi_(x) phase”(x=0.1˜1.5) is phase-changed into a cobalt silicide of “CoSi₂ phase”through the secondary annealing process. Among cobalt silicides, thecobalt silicide of “CoSi₂ phase” has the lowest resistivity.

After the ohmic contact layer 67 is formed, there may be an unreactedsilicidable layer 66A remaining. The volume of the recessed first plugs64B may be reduced as represented by reference numeral “64.”

During the annealing process 67A, since the reaction area of siliconparticipating in the silicidation reaction is increased due to therecessed surface and protrusion of the recessed first plugs 64B, thecobalt silicide of “CoSi₂ phase” having a low resistivity may be formed.When the surface of the first plugs 64A is not recessed, the reactionarea of the silicon participating in the silicidation reaction is soinsufficient that a cobalt silicide of “Co₂Si phase” having a highresistivity may be formed.

As described above, when the cobalt silicide of “CoSi₂ phase” is formedfor the ohmic contact layer 67, not only is the contact resistancedecreased, but also a low-resistance cobalt silicide may be formed evenin the small area of the contact holes 62 having a micro line width.

Referring to FIG. 7H, the unreacted silicidable layer 66A shown in FIG.7G is removed.

Subsequently, second plugs 68A are formed over the ohmic contact layer67. The second plugs 68A may include a metal-containing layer. Thesecond plugs 68A may include a tungsten-containing material. The secondplugs 68A may include a tungsten layer or a tungsten compound layer.

The second plugs 68A may be formed in the same height as the surface ofthe bit line structures 60. The volume of the second plugs 68A isgreater than that of the first plugs 64. The second plugs 68A are formedadjacent to the bit lines 57. The first plugs 64 are not adjacent to thebit lines 57.

As described above, when the second plugs 68A are formed, preliminaryfirst contact plugs are formed. The preliminary first contact plugsinclude the first plugs 64, the ohmic contact layer 67, and the secondplugs 68A.

Referring to FIG. 7I, second contact plugs 69 are formed over the secondplugs 68A. The second contact plugs 69 include a metal-containing layer.The second contact plugs 69 may include a tungsten-containing material.The second contact plugs 69 may include a tungsten layer or a tungstencompound layer. The second contact plugs 69 are formed by etching thetungsten-containing material. A mask pattern (not shown) may be used toform the second contact plugs 69. The second contact plugs 69 may besimultaneously formed along with metal lines in a peripheral circuitregion.

The second contact plugs 69 are a pattern covering a portion of eachsecond plug 68A. Therefore, a portion of the second plug 68A, a portionof the spacer 63, and a portion of the sacrificial spacer 65 areexposed.

Subsequently, recesses 70 are formed. The second plugs 68A exposedbetween the second contact plugs 69 are etched to a predetermined depth.Herein, a portion of the sacrificial spacer 65, a portion of the spacer63, and a portion of the bit line hard mask 58 to are etched to apredetermined depth. Although not illustrated in the drawing, a portionof the second inter-layer dielectric layer 61 between the bit linestructures 60 may be etched.

As described above, the recesses 70 are formed by etching a portion ofeach second plug 68A of each preliminary first contact plug. As aresult, first contact plugs have a stacked structure where the firstplugs 64, the ohmic contact layer 67 and the second plugs 68 arestacked.

Referring to FIG. 7J, air gaps 71 are formed by removing the sacrificialspacers 65. Each air gap 71 is formed between the sidewall of eachsecond plug 68 and the sidewall of each bit line structure 60. Thesacrificial spacers 65 may be removed through a wet etch process. Acleaning process using a wet chemical may be performed to remove thesacrificial spacers 65. The cleaning process may include a post-cleaningprocess that is performed posterior to an etch process for forming thesecond contact plugs 69. In this manner, the sacrificial spacers 65 maybe removed without an additional process.

The sacrificial spacers 65 are removed through the above-describedprocess, and the space occupied by the sacrificial spacers 65 remains asthe air gaps 71.

The air gaps 71 are formed between the sidewalls of each second plug 68and the sidewalls of each bit line structure 60. An insulation structureof ‘air gap 71-spacer 63’ is formed between to the sidewalls of thesecond plug 68 and the sidewalls of the bit line structure 60. The ohmiccontact layer 67 is exposed under the air gaps 71, but the first plugs64 are not exposed.

Since the sacrificial spacers 65 are formed of a silicon oxide and asilicon nitride, the air gaps 71 may be protected from a Not-Openphenomenon and the bit line structures 60 may be prevented from beingdamaged when the sacrificial spacers 65 are removed.

Also, since the air gaps 71 are formed after the etch process forforming the second contact plugs 69, there is no loss in the air gaps71.

Referring to FIG. 7K, a capping layer 72 is formed to cap the secondplugs 68 and the air gaps 71. The capping layer 72 includes a dielectricmaterial. The capping layer 72 may include a dielectric material havinga low step coverage. For example, the capping layer 72 may be formedthrough a Plasma Enhanced Chemical Vapor Deposition (PECVD) process, andaccordingly, the capping layer 72 may dog the entrances of the air gaps71. The capping layer 72 includes a silicon oxide layer or a siliconnitride layer. The capping layer 72 may be a silicon nitride layerformed through the PECVD process.

The capping layer 72 gap-fills the recesses 70 while capping the airgaps 71. Additionally, the capping layer 72 covers the upper portions ofthe second contact plugs 69. The capping layer 72 may be formed byconformally lining a first capping layer then gap-filling a secondcapping layer. The capping layer 72 may be used as an etch stop layer inthe subsequent etch process.

As described above, a portion of each air gap 71 is capped with thesecond contact plug 69, and the other portion of the air gap 71 iscapped with the capping layer 72.

Referring to FIG. 7L, storage nodes 73 are formed over the secondcontact plugs 69. For example, to form the storage nodes 73, asacrificial layer (not shown) is formed over the capping layer 72, thenopenings exposing the second contact plugs 69 are formed by etching thesacrificial layer and the capping layer 72. Subsequently, the storagenodes 73 are formed within the openings, and the sacrificial layer isstripped off. Although not illustrated in the drawing, a dielectriclayer and plate nodes may be formed over the storage nodes 73. Thestorage nodes 73 are of a pillar shape. According to another embodimentof the present invention, the storage nodes 73 may be formed in acylindrical shape. Since the storage nodes 73 are formed over the secondcontact plugs 69, overlap margin may be secured.

As described above, the storage node contact plugs formed between thesubstrate 51 and the storage nodes 73 include first contact plugs 69Aand second contact plugs 69. The first contact plugs 69A include thefirst plugs 64, the ohmic contact layer 67, and the second plugs 68.

The semiconductor device in accordance with the embodiments of thepresent invention may be applied not only to a Dynamic Random AccessMemory (DRAM) device, but also to a Static Random Access Memory (SRAM)device, a flash memory device, a Ferroelectric Random Access Memory(FeRAM) device, a Magnetic Random Access Memory (MRAM) device, aPhase-change Random Access Memory (PRAM) device, and so forth.

FIG. 8 illustrates a memory card.

Referring to FIG. 8, the memory card 400 includes a memory controller410 and a memory device 420. The memory controller 410 and the memorydevice 420 may exchange electrical signals with each other.Specifically, the memory controller 410 and the memory device 420exchange data with each other at the command of the memory controller410. Accordingly, the memory card 400 stores a data in the memory device420 or outputs the data from the memory device 420 to the outside. Thememory device 420 may include a semiconductor device including air gaps,which are described above. The memory card 400 may be used as a datastorage medium for diverse portable devices. For example, the memorycard 400 may include a memory stick card, a smart media card (SM), asecure digital card (SD), a mini secure digital card (mini-SD), amultimedia card (MMC) and so forth.

FIG. 9 illustrates an electronic system.

Referring to FIG. 9, the electronic system 500 may include a processor510, an input/output device 530, and a chip 520. The processor 510, theinput/output device 530, and the chip 520 may perform data communicationwith each other through a bus 540. The processor 510 runs a program, andcontrols the electronic system 500. The input/output device 530 is usedto input or output a data to or from the electronic system 500. Theelectronic system 500 is connected to an external device, such as apersonal computer or a network, and exchanges data with the externaldevice by using the input/output device 530. The chip 520 may store acode or a data for the operation of the processor 510, and process apart of the operation ordered by the processor 510. For example, thechip 520 may include a memory device including a semiconductor devicewith the air gaps described above. The electronic system 500 maycomprise diverse electronic control devices in need of the chip 520. Forexample, the electronic system 500 may be used for a mobile device, anMP3 player, a navigator, a solid state disk (SSD), household appliancesand so on. The electronic system 500 may further include an applicationchipset, an image signal processor, and/or a modem.

The technology of the present invention may decrease both parasiticcapacitance and contact resistance by stably capping the air gap.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: forming an isolation layer over a substrate; forming anopening by etching the isolation layer; forming a preliminary firstconductive structure which includes a first conductive structure formedinside the opening and a sacrificial spacer formed between a sidewall ofthe first conductive structure and a side all of the opening; forming asecond conductive structure which covers a portion of the firstconductive structure and a portion of the sacrificial spacer; forming anair gap by removing the sacrificial spacer; and forming a cappingstructure for capping a portion of the air gap.
 2. The method of claim1, further comprising: forming a recess by etching the preliminary firstconductive structure to be self-aligned to an edge of the secondconductive structure, before the forming of the air gap.
 3. The methodof claim 1, wherein the capping structure includes a dielectricmaterial.
 4. The method of claim 1, wherein the forming of thepreliminary first conductive structure includes: forming a firstconductive pattern recessed in the opening; forming a second conductivepattern over the first conductive pattern; forming the sacrificialspacer on the sidewall of the opening over the first conductive pattern;forming a second conductive pattern over e first conductive pattern; andforming a third conductive pattern which fills the opening over thesecond conductive pattern and the sacrificial spacer.
 5. The method ofclaim 4, wherein the second conductive pattern includes a metalsilicide, and the first conductive pattern includes a silicon-containinglayer, and the third conductive pattern includes a metal-containinglayer.
 6. The method of claim 1, wherein the first conductive structureand the second conductive structure include plugs.
 7. A method forfabricating a semiconductor device, comprising: forming a plurality offirst conductive structures over a substrate; forming an isolation layerbetween the multiple first conductive structures; forming openings byetching the isolation layer; forming preliminary second conductivestructures each of which includes a second conductive structure formedinside each opening and a sacrificial spacer formed between a sidewallof the second conductive structure and a sidewall of the opening;forming a third conductive structure which covers a portion of eachsecond conductive structure and a portion of each sacrificial spacer;forming air gaps by removing the sacrificial spacers; and formingcapping structures for capping the air gaps.
 8. The method of claim 7,further comprising: forming recesses by etching the second conductivestructures and the sacrificial spacers to be self-aligned to an edge ofeach third conductive structure, before the forming of the air gaps. 9.The method of claim 7, wherein the capping structures include andielectric material.
 10. The method of claim 7, wherein the forming ofthe preliminary second conductive structures includes: forming a firstconductive pattern recessed in the openings; forming a second conductivepattern over the first conductive pattern; forming the sacrificialspacer on a sidewall of each opening over the second conductive pattern;and forming a third conductive pattern which fills the openings over thesecond conductive pattern and the sacrificial spacers.
 11. The method ofclaim 10, wherein the second conductive pattern includes a metalsilicide, and the first conductive pattern includes a silicon-containinglayer, and the third conductive pattern includes a metal-containinglayer.
 12. The method of claim 7, wherein the first conductivestructures and the second conductive structures include plugs.
 13. Amethod for fabricating a semiconductor device, comprising: forming aplurality of bit line structures over a substrate; forming aninter-layer dielectric layer between the multiple bit line structures;forming contact holes by etching the inter-layer dielectric layer;forming preliminary first conductive structures each of which includes afirst plug structure formed inside each contact hole and a sacrificialspacer formed between a sidewall of the first plug structure and asidewall of the contact hole; forming second plug structures each ofwhich covers a portion of each first plug structure and a portion ofeach sacrificial spacer; forming recesses by etching the first plugstructures and the sacrificial spacers to be self-aligned to an edge ofthe second plug structure; forming air gaps by removing the sacrificialspacers; and forming capping structures for capping the recesses and theair gaps over a substrate structure including the second plugstructures.
 14. The method of claim 13, further comprising: formingcapacitors each of which includes a storage node that penetrates througheach capping structure to be coupled with the second plug structure,after the forming of the capping structures.
 15. The method of claim 1further comprising: forming buried gate-type transistors each of whichincludes a gate electrode buried in the substrate, before the forming ofthe first conductive structures.
 16. The method of claim 13, wherein thecapping structures include an dielectric material.
 17. The method ofclaim 13, wherein the forming of the preliminary first plug structuresincludes: forming first plugs recessed in the contact holes; forming anohmic contact layer over the first plugs; forming the sacrificialspacers on the sidewall of the contact holes over the ohmic contactlayer; and forming second plugs which fill the contact holes over theohmic contact layer and the sacrificial spacers.
 18. The method of claim17, wherein the ohmic contact layer includes a metal silicide, and thefirst plugs include a silicon-containing layer, and the second plugsinclude a metal-containing layer.